Certain objects, such as data entry keyboards for use in connection with a computer and visual monitors, have been mounted on a support surface formed on an adjustable support apparatus that permits varying the height, as well as the inclination, of the support surface. Varying the height and inclination of the object reduces strain on the user. For example, varying the height and inclination of a keyboard permits its positioning to be adapted to the characteristics and preferences of the user and can prevent carpel tunnel syndrome.
In the past, apparatus for supporting keyboards have included an arm, the proximal end of which is rotatably mounted on a base that can be affixed to the underside of a desk. A support plate, on which the keyboard is mounted, is rotatably mounted on the distal end of the arm. Rotating the arm up or down at the base allows the height of the keyboard to be adjusted, while rotation of the support plate on the arm allows the inclination of the keyboard to be adjusted. Unfortunately, such apparatus suffer from several important drawbacks.
The first drawback concerns the locking of the orientation set by the apparatus. Various locking mechanisms have been used to lock the support arm and support plate in the desired orientation. Unfortunately, these mechanisms typically require operation of two or more knobs or levers to effect complete locking or unlocking--for example, one knob to lock/unlock the arm and another to lock/unlock the support plate. This makes adjustment of the apparatus more cumbersome.
The second drawback arises because traditional methods for mounting the support plate to the support arm cause the inclination of the support plate to vary as the arm is rotated up and down. Thus, although the user will often desire to maintain a constant, horizontal inclination for the keyboard, the resetting of the height of the keyboard will necessitate resetting the inclination to maintain the keyboard horizontal.
The third drawback concerns restraining the downward motion of the support arm. If unrestrained, the weight load resulting from the combined weight of the support arm, support plate and keyboard creates a downward wight moment that can cause the support plate to drop very rapidly when the arm locking mechanism is disengaged. This could result in the keyboard striking the user or otherwise cause injury to the user or damage to the equipment. Consequently, various mechanisms have been used to restrain the downward motion of the arm.
One approach involves the use of a torsion spring that applies a moment that opposes the weight moment by tending to rotate the support arm upward. Unfortunately, the moment applied by a torsion spring is more or less linearly proportional to the angular orientation of the support arm. This is in contrast to the moment applied by the supported weight, which initially increases as the arm is rotated upward from its minimum height position, reaching a maximum when the arm is extended horizontally, and then decreases as the arm is further rotated to its maximum height. Thus, if a torsion spring is arranged to provide adequate force to offset the maximum weight moment when the arm is horizontal, as well as to provide at least some force when the arm is near its raised position, the upward force it will apply when the arm is in the lowered position can become excessive.
Another approach involves the use of a gas filled cylinder, similar to those used to restrain downward motion of the tailgate or hatch back in an automobile, which produces a substantially constant force. However, as heretofore used, the opposing moment resulting from gas filled cylinders did not match that of the weight moment as the arm rotated over its range of orientations so as to be a maximum value when the arm was horizontal, and weight moment a maximum, and a minimum value when the arm was rotated into its maximum or minimum height orientations, when the weight moment was at a minimum value.
Recently, it has been proposed that support apparatus for use in conjunction with data entry keyboards be capable of supporting the keyboard in positions that allow it to be used both when the user is seated and when standing. It is thought that affording brief opportunities for standing provide a respite that will enhance the productivity of data entry personnel. Achieving this objective will require a larger range of support plate heights, as compared to apparatus used only in the seated position. This, in turn, will require a longer support arm, which will result in a larger maximum moment as a result of the weight load, as well as a much larger difference between the maximum and minimum moments. In such applications, the failure of conventional approaches to more closely match the opposing moment to the weight moment is especially undesirable.
Consequently, it would be desirable to provide an adjustable support apparatus for an object, such as a keyboard or a visual monitor, that allowed both the height and inclination locking mechanisms to be engaged and disengaged by a single operation of the user's hand, that allowed the inclination of the support to be maintained constant throughout the range of vertical motion, and that provided for smoother and safer operation by creating an opposing moment that more closely matched the moment resulting from the supported weight.